Drag chains employed in the cement industry encounter a hostile abrasive environment tending to produce rapid wear. Cement is primarily made of limestone, and hard igneous rock materials in rotary kilns. Kilns are fired at one end heating the materials which mixes under the rotary action of the kiln, progresses through four chemical reactions at high temperatures and emerges as cement clinker at the output end. After this, the clinker is cooled and moved to the ball mills. A sequence of drag links joined to each other by pins comprise the endless drag chain which is driven by a sprocket and conveys the abrasive material along the bottom of a trough to the ball mills for final grinding.
Each link of the drag chain has a barrel at one end with side arms extending lengthwise and outward sufficient to reach the barrel of the next link. A pintle pin crosses through a hole in the barrel of one link and boss holes in the extremities of the two side arms of the next link to connect the successive identical cast drag links and form the endless drag chain. Conventional pintle pins are normally constructed of uniform diameter steel rod headed at one end with a headed locking pin inserted in a crosshole at the other end and retained by a cotter pin. The rods normally have loose fits in all of the link holes through which they pass and are particularly vulnerable to the introduction of abrasive grit near the ends of the pins in the holes in the exposed bosses on the extremities of the arms of the drag links. Excessive wear occurs there between the ends of the pins and the side arm boss holes of the links engaged by such ends.